FWIW here is a post from the old TOMM Forum on 25/ 9/07 by Bok Choy Baby, who points out that Whitworth threads were common on old engines from various countries, sometimes in conjunction with metric hexes and sometimes with Whitworth hexes. I have struck Whitworth threads several times in unexpected places on old Continental vehicles and machinery. While he does not specifically mention Italy, it is possible that some Italian manufacturers may have used Whitworth threads - after all, they were the first standard thread, and were in general use world wide in British manufactured machinery.
"Actually threads are an important part of identifying an engine. I often see people trying to identify engines on forums like this or in magazines, what they always fail to provide is information about thread type and sizes.
It is a simple fact that the majority of French built engines have metric hexes and threads. Whereas early German and Swiss engines are normally built with metric hexes and whitworth threads. Tangyes was using smaller hexes on their engines compared to other English makers in the 1890s. Swedish engines use whitworth hexes and whitworth threads."
It is also possible that in the case of this engine, the driven item, if from from a different manufacturer, might have been fitted in Britain or Australia where Whitworth was the standard thread for almost every application, after the engine had been delivered locally.
Frank.
